Electroluminescent devices using organic materials (hereinafter, simply referred to as an “organic EL device”) have been extensively developed in expectation of their use as solid-state luminescent devices or emitting devices for use in inexpensive large full-color displays.
In general, such an organic EL device has a structure in which a light emitting layer is provided between a cathode and an anode. When an electric field is applied between the cathode and the anode, electrons are injected into the light emitting layer from the cathode side, and holes are injected into the light emitting layer from the anode side.
The injected electrons and holes are recombined in the light emitting layer, which then causes their energy level to return from the conduction band to the valence band. At this time, excitation energy is released as light energy so that the light emitting layer emits light.
In such organic EL devices, it has been known that a layered device structure, in which organic layers formed of organic materials having different carrier transport properties for electrons or holes are provided between a light emitting layer and a cathode and/or an anode, is effective in obtaining a high-efficiency organic EL device with high luminance.
For this purpose, it is necessary to laminate a light emitting layer and organic layers having different carrier transport properties from each other (hereinafter, these layers are collectively referred to as “organic layers”) on the electrode. However, in the conventional manufacturing method using an application method, when such organic layers are laminated, mutual dissolution occurs between the adjacent organic layers, thereby causing the problem of deterioration in the light emitting efficiency of a resultant organic EL device, the color purity of emitted light, and/or the pattern precision.
For this reason, in the case where organic layers are laminated, these organic layers have to be formed using organic materials having different solubilities.
In order to solve such a problem, a method for improving the durability of a lower organic layer, that is, the solvent resistance of the lower organic layer has been disclosed (see, for example, JP-A No. 9-255774). In this method, organic materials constituting the lower organic layer are polymerized to improve the solvent resistance of the lower organic layer.
Another method for improving the solvent resistance of a lower organic layer is found in JP-A No. 2000-208254. This publication discloses a method in which a curing resin is added to an organic material constituting the lower organic layer to cure the organic material together with the curing resin.
However, even in the case where such a method is employed in manufacturing an organic EL device, the characteristics of the resultant organic EL device are not so improved as to meet expectations in actuality.
The problem described above has also been raised in thin film transistors using organic materials.